Margin after automic line break will be ignored - css

Question

The margin takes only affect for the first line (after automatic line break (depends on the size) will be ignored).
The HTML:
<div class="BWForm_form-group">
<div class="col-md-3 BWTextLeft">
<label class="control-label" for="ContactPersonName">Name des Ansprechpartners<span style="color:red; display: inline-block;"> *</span></label>
</div>
<div class="col-md-5">
<div class="col-md-12">
<input class="text-box single-line input-validation-error" data-val="true" data-val-required="The Name of contact person field is required." id="ContactPersonName" name="ContactPersonName" value="" type="text">
</div>
</div>
<div class="col-md-4">
<span class="field-validation-error" data-valmsg-for="ContactPersonName" data-valmsg-replace="true"><span class="" for="ContactPersonName">The Name of contact person field is required.</span></span>
</div>
</div>
The css:
.field-validation-error {
color: #B94A48;
font-weight: bold;
margin: 15px;
}
The "BWForm_form-group" is inherited by the bootstrap class form-group."BWTextLeft" will only align:left.
What can I do to fix it ?
It looks like that click (the problem is right to my green arrow and vertical line)
Ty for helping

Answer 1

oh ok remove the margin left from field-validation-error and then add a new class like to the container
<div class="col-md-12 custom">
and the css looks like the below
custom {
margin:15px;
}
demo example here
if you dont want to mess with the margins of the col-md-12 then you should add a surrounding div like this
<div class="col-md-12">
<div class="custom">
<div class="field-validation-error">